A brush motor includes a commutator mounted on a rotor, and at least one pair of brushes mounted on a stator. The commutator is electrically connected with windings of the rotor. The brushes are arranged to slidably contact segments of the commutator to provide power to the rotor. Usually, the number of pairs of brushes is equal to the number of pairs of stator poles.
Referring to FIG. 9, a typical six-pole, nine-slot brush motor is shown in developed view. The windings of the motor includes 18 coils 80 wound around nine teeth T1-T9 of a stator. The commutator of the motor includes 18 segments S1-S18 electrically with the coils 80. The motor further includes a plurality of equalizing wires e1 -e6, each of which electrically connects multiple equipotential segments S1-S18, such that the voltage of the multiple equipotential segments are the same. That is, the equalizing wires e1-e6 can replace one or more pairs of brushes. Thus, the number of pairs of brushes can be reduced by using the equalizing wires. The brushes are not shown in FIG. 9.
Referring to FIG. 10, the motor is only equipped with one pair of brushes 71 and 72. When the brushes 71, 72 respectively contact the segments S1 and S10, the segments S7 and S13 each have a potential equal to that of the segment S1 as the segments S1, S7 and S13 are electrically connected together by the equalizing wire e1. The segments S4 and S16 each have a potential equal to that of the segment S10 as the segments S4, S10 and S16 are electrically connected together by the equalizing wire e4. Therefore, six parallel circuits are formed in the windings, and each parallel circuit includes three coils 80 electrically connected in series. Arrows in FIG. 10 show direction of the current flowing in the coils 80. Suppose the strength of the current in each parallel circuit is I, the strength of the current flowing in the equalizing wire e1 connected between the segments S1 and S7 is thus 4I, the current flowing in the equalizing wire e1 is too large, which may result in a high risk of fusing the equalizing wire e1.
FIG. 11 shows the motor equipped with two further brushes 73, 74. Also suppose the strength of the current in each parallel circuit is I, the strength of the current flowing in the equalizing wire el connected between the segments S7 and S13 is thus 2I, the current flowing in the equalizing wire is also too large although another pair of brushes 73, 74 has been added.
Therefore, there is a need in the art to provide an improved brush motor which has a low risk of fusing the equalizing wires.